Preface: This post is still extremely draft and dis-organised. It’s part of an evolving concept development and at this point in time serves more to document research findings and decisions. It will, in time be cleaned up and more fit for public presentation.
I’ve been thinking for a while now that a self-steering wind vane system is high on the list of priorities for ‘Blue.
There are many reasons for doing all the work on your boat yourself. One is obviously the cost but another really big motivation is the detailed knowledge and understanding you gain of the boat. When something goes wrong out yonder, which it will, you want to have a clear understanding of what it would take to jury-rig a fix.
With the hardware stores and chandleries closed there is no chance of building a prototype. Not that a prototype could be built right now even if the materials were available because the design is not yet started. So, what better time to conduct the research needed to make a decision and finalise the concept?
There are many variations of the theme out there but for our purposes the story is narrowed down to two basic options: trim tab or servo pendulum.
A trim tab system is simpler, easier to construct than a servo and there is plenty of evidence that it works admirably well [How to sail oceans, Pardey]. Chatting to the previous skipper of Jigsaw about his Pacific crossing I recall the following tale…..
“There was this Miura coming up a-stern of us, much faster than us obviously because shes 31 feet versus our 26 feet, but here’s the thing… She was first visible off the port quarter then, next we looked she was off the starboard quarter. For miles and miles as she reeled us in and overtook us she jig-zagged her way down the trades, struggling to keep a straight course whereas Jigsaw tracked straight and true with her servo pendulum system. When we later met up with them at one of the downwind anchorages we learned they had a trim tab steering system on board.”
The above story has had me thinking for a while now but I think the penny has finally dropped. I have a theory. The Ruth Avery’s and the Taillesin’s of this world are medium to heavy displacement full keel boats, designs particularly well suited to tracking straight and true in a seaway. The Miura in the Jigsaw tale is a fin keeler with a transom-hung rudder and while she’s a solid, well respected sailboat, comparing a long keel to a fin keel in terms of straightline stability is like comparing giraffes and porcupines.
So, a trim tab system, while relatively simple to fabricate at home with limited DIY skills, is probably not the best choice….
The traditional servo-pendulum system is most definitely the most-praised self steerer out there. There are many commercial systems to choose from but even the cheapest cost about half of what my good old mid-70’s boat is worth. Even if you did buy an off-the-shelf unit, there’s still the stainless frame required to mount the servo blade off the transom, there’s the vane mounting, the linkages between the two, the control lines running to the tiller. So, even if a commercial system is acquired, there’s still a crap-ton of modification and work to be done to customise the installation to suit the particular boat.
So it was with some glimmer of hope that I stumbled across the concept of the RHM self steerer. RHM stands for Rudder Head Mount meaning exactly that…the servo rudder is mounted directly to the rudder head. Obviously this won’t work on all boats but for ‘Blue, with her tiller steering and transom-hung rudder, it seems this design is the answer to the prayer.
|Considering the options….||
|Modifications to rudder below the waterline||Yes||No||No|
|Stainless framework on transom||No||Yes||No|
|Best power and performance for a fin-keeler based on anecdotal evidence||Acceptable||Best||Acceptable|
|Can be built at home without welding skills||Yes||No||Yes|
Some initial design concept thoughts:
- My biggest mental dilemma thus far has been on how to fabricate the interface between vane and servo. Many systems, and indeed all commercial systems, use a direct mechanical linkage, some geared, others via linkages. Watching Wave Rover posed the solution – control lines.
Things to consider:
- Integration with existing electronic autopilot.
- Servo blade stowage for motoring, reversing, storage.
- Vane: angled or 90 degrees [see Wave Rover]. 90o is certainly easier to build.
- Adjustments in operation: vane angle of attack, vane angle from vertical, control line positions, system damping.
- Strength vs weight
- USD vane or traditional?
Jan Alkema’s genius, further developed by Walt Murray….
I’m still unsure of the dimension ratios. Are they there because of the direct linkages? If I use adjutable control lines on blocks do I need to pay attention to the exact ratios?
Wave Rover samples
Wave Rover is a Contessa 26, another long-keel yacht. She uses a trim tab system
Free Range Sailing have a good idea for the autopilot-self-steerer interface…